Retirement Benefits - Changes in Projected Benefit Obligations and Fair Value of Plan Assets (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension Plans [Member]
Change in benefit obligation
Benefit obligation at beginning of year	$ 8,863,000	$ 9,302,000
Service cost	213,000	232,000	198,000
Interest cost	435,000	389,000	393,000
Benefits paid	(382,000)	(357,000)
Actuarial loss (gain)	1,780,000	(703,000)
Balance at end of year	10,909,000	8,863,000	9,302,000
Change in plan assets
Fair value of plan assets at beginning of year	8,733,000	7,953,000
Actual return (loss) on plan assets	797,000	1,098,000
Employer contributions	542,000	39,000
Fair value of plan assets at end of year	9,690,000	8,733,000	7,953,000
Accrued liability	(1,219,000)	(130,000)
Other Postretirement Benefits [Member]
Change in benefit obligation
Benefit obligation at beginning of year	1,682,000	1,872,000
Service cost	21,000	24,000	21,000
Interest cost	79,000	74,000	85,000
Benefits paid	(102,000)	(94,000)
Plan amendments	(2,000)	0
Actuarial loss (gain)	300,000	(200,000)
Retiree drug subsidy	8,000	6,000
Balance at end of year	1,986,000	1,682,000	1,872,000
Change in plan assets
Fair value of plan assets at beginning of year	901,000	821,000
Actual return (loss) on plan assets	54,000	129,000
Employer contributions	39,000	39,000
Benefits paid, net of drug subsidy	(94,000)	(88,000)
Fair value of plan assets at end of year	900,000	901,000	821,000
Accrued liability	(1,086,000)	(781,000)
Alabama Power [Member] \| Pension Plans [Member]
Change in benefit obligation
Benefit obligation at beginning of year	2,112,000	2,218,000
Service cost	48,000	52,000	44,000
Interest cost	103,000	93,000	94,000
Benefits paid	(100,000)	(93,000)
Actuarial loss (gain)	429,000	(158,000)
Balance at end of year	2,592,000	2,112,000	2,218,000
Change in plan assets
Fair value of plan assets at beginning of year	2,278,000	2,077,000
Actual return (loss) on plan assets	207,000	285,000
Employer contributions	11,000	9,000
Fair value of plan assets at end of year	2,396,000	2,278,000	2,077,000
Accrued liability	(196,000)	166,000
Alabama Power [Member] \| Other Postretirement Benefits [Member]
Change in benefit obligation
Benefit obligation at beginning of year	431,000	490,000
Service cost	5,000	6,000	5,000
Interest cost	20,000	19,000	22,000
Benefits paid	(27,000)	(24,000)
Actuarial loss (gain)	71,000	(62,000)
Retiree drug subsidy	3,000	2,000
Balance at end of year	503,000	431,000	490,000
Change in plan assets
Fair value of plan assets at beginning of year	389,000	343,000
Actual return (loss) on plan assets	23,000	61,000
Employer contributions	4,000	7,000
Benefits paid, net of drug subsidy	(24,000)	(22,000)
Fair value of plan assets at end of year	392,000	389,000	343,000
Accrued liability	(111,000)	(42,000)
Georgia Power [Member] \| Pension Plans [Member]
Change in benefit obligation
Benefit obligation at beginning of year	3,116,000	3,312,000
Service cost	62,000	69,000	60,000
Interest cost	153,000	138,000	141,000
Benefits paid	(149,000)	(141,000)
Actuarial loss (gain)	599,000	(262,000)
Balance at end of year	3,781,000	3,116,000	3,312,000
Change in plan assets
Fair value of plan assets at beginning of year	3,085,000	2,827,000
Actual return (loss) on plan assets	285,000	387,000
Employer contributions	162,000	12,000
Fair value of plan assets at end of year	3,383,000	3,085,000	2,827,000
Accrued liability	(398,000)	(31,000)
Georgia Power [Member] \| Other Postretirement Benefits [Member]
Change in benefit obligation
Benefit obligation at beginning of year	723,000	800,000
Service cost	6,000	7,000	7,000
Interest cost	34,000	31,000	37,000
Benefits paid	(44,000)	(45,000)
Actuarial loss (gain)	142,000	(73,000)
Retiree drug subsidy	3,000	3,000
Balance at end of year	864,000	723,000	800,000
Change in plan assets
Fair value of plan assets at beginning of year	407,000	382,000
Actual return (loss) on plan assets	21,000	56,000
Employer contributions	8,000	11,000
Benefits paid, net of drug subsidy	(41,000)	(42,000)
Fair value of plan assets at end of year	395,000	407,000	382,000
Accrued liability	(469,000)	(316,000)
Gulf Power [Member]
Change in benefit obligation
Service cost	10,181	11,128	9,101
Interest cost	19,433	17,321	17,199
Gulf Power [Member] \| Pension Plans [Member]
Change in benefit obligation
Benefit obligation at beginning of year	395,328	413,501
Service cost	10,181	11,128
Interest cost	19,433	17,321
Benefits paid	(15,635)	(14,831)
Actuarial loss (gain)	81,254	(31,791)
Balance at end of year	490,561	395,328
Change in plan assets
Fair value of plan assets at beginning of year	385,639	350,260
Actual return (loss) on plan assets	33,512	49,076
Employer contributions	31,251	1,134
Fair value of plan assets at end of year	434,767	385,639
Accrued liability	(55,794)	(9,689)
Gulf Power [Member] \| Other Postretirement Benefits [Member]
Change in benefit obligation
Benefit obligation at beginning of year	68,579	75,395
Service cost	1,163	1,355	1,167
Interest cost	3,235	2,982	3,367
Benefits paid	(4,061)	(3,583)
Plan amendments	(2,089)	0
Actuarial loss (gain)	11,317	(7,900)
Retiree drug subsidy	357	330
Balance at end of year	78,501	68,579	75,395
Change in plan assets
Fair value of plan assets at beginning of year	17,474	16,227
Actual return (loss) on plan assets	1,578	2,119
Employer contributions	2,846	2,381
Benefits paid, net of drug subsidy	(3,704)	(3,253)
Fair value of plan assets at end of year	18,194	17,474	16,227
Accrued liability	(60,307)	(51,105)
Mississippi Power [Member]
Change in benefit obligation
Service cost	10,123	11,067	9,416
Interest cost	20,093	18,062	18,019
Change in plan assets
Employer contributions	4,600	4,100	3,900
Mississippi Power [Member] \| Pension Plans [Member]
Change in benefit obligation
Benefit obligation at beginning of year	409,395	432,553
Service cost	10,123	11,067
Interest cost	20,093	18,062
Benefits paid	(17,499)	(16,207)
Actuarial loss (gain)	90,735	(36,080)
Balance at end of year	512,847	409,395
Change in plan assets
Fair value of plan assets at beginning of year	387,403	351,749
Actual return (loss) on plan assets	40,051	49,431
Employer contributions	35,526	2,430
Fair value of plan assets at end of year	445,481	387,403
Accrued liability	(67,366)	(21,992)
Mississippi Power [Member] \| Other Postretirement Benefits [Member]
Change in benefit obligation
Benefit obligation at beginning of year	80,940	91,783
Service cost	1,025	1,151	1,038
Interest cost	3,812	3,619	4,155
Benefits paid	(4,887)	(4,080)
Actuarial loss (gain)	14,259	(11,959)
Retiree drug subsidy	506	426
Balance at end of year	95,655	80,940	91,783
Change in plan assets
Fair value of plan assets at beginning of year	23,277	21,990
Actual return (loss) on plan assets	1,814	2,379
Employer contributions	3,413	2,562
Benefits paid, net of drug subsidy	(4,381)	(3,654)
Fair value of plan assets at end of year	24,123	23,277	21,990
Accrued liability	$ (71,532)	$ (57,663)

Benefits paid net of drug subsidy.

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The difference between fair value of plan assets at the end of the period and the fair value at the beginning of the period, adjusted for contributions and payments of benefits during the period, and after adjusting for taxes and other expenses, as applicable.

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-Glossary Actual Return on Plan Assets (Component of Net Periodic Postretirement Benefit Cost)

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Amount of gain (loss) related to change in benefit obligation resulting from changes in actuarial assumptions, for example, but not limited to, interest, mortality, employee turnover, salary, and temporary deviation from the substantive plan.

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1) For defined benefit pension plans, the benefit obligation is the projected benefit obligation, which is the actuarial present value as of a date of all benefits attributed by the pension benefit formula to employee service rendered prior to that date. 2) For other postretirement defined benefit plans, the benefit obligation is the accumulated postretirement benefit obligation, which is the actuarial present value of benefits attributed to employee service rendered to a particular date.

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-Glossary Projected Benefit Obligation

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-Glossary Accumulated Postretirement Benefit Obligation

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The amount of payments made for which participants are entitled under a pension plan, including pension benefits, death benefits, and benefits due on termination of employment. Also includes payments made under a postretirement benefit plan, including prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. This item represents a periodic decrease to the plan obligations and a decrease to plan assets.

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The increase in the fair value of plan assets from contributions made by the employer.

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Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.

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The funded status is measured as the difference between the fair value of plan assets and the benefit obligation. Will normally be the same as the net Defined Benefit Plan, Amounts Recognized in Balance Sheet, Total.

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Amount of the period's gross receipts received from the prescription drug subsidy, which is to be used in the roll forward of the accumulated postretirement benefit obligation of an applicable postretirement benefit plan.

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The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.

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The amount of increase or decrease due to a change in the terms of an existing plan or the initiation of a new plan. A plan amendment may increase or decrease benefits, including those attributed to years of service already rendered.

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The actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan.

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